The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Environmentally-friendly techniques of vehicles are very important and the survival of future motor industry is dependent thereon. Vehicle makers are focusing on development of environmentally-friendly vehicles so as to meet environmental and fuel consumption regulations.
Some examples of future vehicle techniques are a hybrid electric vehicle (HEV) and a dual clutch transmission (DCT).
The hybrid electric vehicle uses an internal combustion engine and a battery power source together. In other words, the hybrid electric vehicle efficiently combines and uses torque of the internal combustion engine and torque of a driving motor. Since the hybrid electric vehicle uses both of mechanical energy of the engine and electrical energy of the battery, desired operation regions of the engine and the motor may be used, and energy upon braking may be recovered, such that fuel efficiency may be improved and energy may be efficiently used.
The hybrid electric vehicle provides driving in an electric vehicle (EV) mode in which only torque of the driving motor is used; a hybrid electric vehicle (HEV) mode in which torque of the engine is used as main torque and torque of the driving motor is used as auxiliary torque; and a regenerative braking mode in which braking and inertial energy are recovered through electrical power generation of the driving motor during braking of the vehicle or during deceleration of the vehicle by inertia to be charged in the battery.
The DCT includes two clutches and a gear train applied to a manual transmission. The DCT selectively transmits torque output from a torque source (e.g., engine or driving motor) to two input shafts by using two clutches, changes a speed by using the gear train, and outputs the changed torque.
The DCT is used to realize a compact transmission having five or more forward speed stages. Since two clutches and synchronizers are controlled by a controller, a manual shift maneuver may be unnecessary for controlling the DCT. Therefore, the DCT is one type of automated manual transmission (AMT).
In the case of an automatic transmission, shifting is achieved by operation of friction elements (clutches and brakes) including a planetary gear train.
In contrast, in the case of the DCT, the shifting is achieved by operation of a shift clutch corresponding to a target gear stage after a speed gear corresponding to the target gear stage is connected to an output shaft corresponding to the target gear stage. Therefore, a speed gear corresponding to a next gear stage is connected to an output shaft corresponding to the next gear stage in advance so as to secure shift responsiveness, which is called a pre-selection (or pre-engagement). However, since a rotation shaft of the DCT is restricted when the pre-selection is performed, power delivery performance and fuel efficiency are deteriorated due to a drag loss. In other words, since the shift responsiveness and the fuel efficiency are in a trade-off relationship, it is difficult to achieve both of them.
Particularly, in the case of the hybrid electric vehicle, when the pre-selection is not unconditionally performed in the regenerative braking mode, shifting time is lengthened, and thus driving points (torque and speed) of the driving motor are deviated from a region where regeneration efficiency of the driving motor is high. When the pre-selection is unconditionally performed in the regenerative braking mode, the fuel efficiency is deteriorated due to the drag loss.